CPP-474: cass_session_get_schema_meta method comment refers to non-existent cass_schema_free method
CPP-474: cass_session_get_schema_meta method comment refers to non-existent cass_schema_free method

* Replaced cass_schema_free ref with cass_schema_meta_free
* Removed irrelevant @see from cass_session_get_metrics, per review feedback.

datastax/cpp-driver,mikefero/cpp-driver,mikefero/cpp-driver,datastax/cpp-driver,mikefero/cpp-driver,mikefero/cpp-driver,mikefero/cpp-driver,datastax/cpp-driver,datastax/cpp-driver